Variable radius under module balanced bearing

ABSTRACT

A solar tracker bearing and a solar tracker incorporating the bearing, the bearing including at least one rotatable part, the rotatable part including a notch for receiving a torque tube, a slot, formed in the rotatable part and extending below the notch, the slot defining an arc having multiple radii, at least one engagement member configured to be received in the slot, and at least one base configured to secure the engagement member in the slot and to secure the bearing to a pier.

BACKGROUND Technical Field

The present disclosure relates to solar power generation systems, andmore particularly, to solar tracker actuating systems for adjusting theorientation of the solar power generation components to track thelocation of the sun.

Background of Related Art

Solar cells and solar panels are most efficient in sunny conditions whenoriented towards the sun at a certain angle. Many solar panel systemsare designed in combination with solar trackers, which follow the sun'strajectory across the sky from east to west in order to maximize theelectrical generation capabilities of the systems. The relatively lowenergy produced by a single solar cell requires the use of thousands ofsolar cells, arranged in an array, to generate energy in sufficientmagnitude to be usable, for example as part of an energy grid. As aresult, solar trackers have been developed that are quite large,spanning hundreds of feet in length.

Adjusting massive solar trackers requires power to drive the solar arrayas it follows the sun. As will be appreciated, the greater the load, thegreater the amount of power necessary to drive the solar tracker. Anadditional design constraint of such systems is the rigidity required toaccommodate the weight of the solar arrays and at times significant windloading.

Further, the torsional excitation caused by wind loading exertssignificant force upon the structure for supporting and the mechanismsfor articulating the solar tracker. As such, increases in the size andnumber of components to reduce torsional excitation are required atvarying locations along the length of the solar tracker. The presentdisclosure seeks to address the shortcomings of prior tracker systems.

SUMMARY

One aspect of the disclosure is directed to a solar tracker bearingincluding: a first rotatable part, the rotatable part including a notchfor receiving a torque tube; a slot, formed in the rotatable part andextending below the notch, the slot defining an arc having multipleradii; a first engagement member configured to be received in the slot;and at least one base configured to secure the engagement member in theslot and to secure the bearing to a pier.

Implementations of this aspect of the disclosure may include one or moreof the following features. The solar tracker bearing where the slotincludes a first radius at a bottom portion of the rotatable part, and asecond radius proximate at least one termination of the slot where thesecond radius is smaller than the first radius. The solar trackerbearing further including a third radius proximate a second termination,where the third radius is larger than the first radius. The solartracker bearing further including a third radius proximate a secondtermination, where the third radius opposes the first radius. The solartracker bearing where the slot includes a first radius at a bottomportion of the rotatable part, and a second radius proximate at leastone termination of the slot where the second radius is larger than thefirst radius. The solar tracker bearing where the slot includes a firstradius at a bottom portion of the rotatable part, and a second radiusproximate at least one termination of the slot where the second opposesthe first radius. The solar tracker bearing further including a secondrotatable part including a notch for receiving the torque tube. Thesolar tracker bearing where the second rotatable part includes a secondslot extending below the notch and defining an arc having multipleradii, where the slot in the first rotatable part matches the slot inthe second rotatable part. The solar tracker bearing further includingat least a second engagement member. The solar tracker bearing where thefirst and second engagement member are received in a u-channel supportedby the base to secure the first and second engagement members in theirrespective slots in the respective rotatable parts. The solar trackerbearing where the first and second engagement members each include twoengagement members. The solar tracker bearing where each of the firstand second rotatable parts include an actuator arm. The solar trackerbearing where the first and second rotatable parts are separated fromone another by a gap. The solar tracker bearing where the gap isconfigured to receive a gear box of an articulation system. The solartracker including a notch offset from a centerline of the rotatablepart. The solar tracker bearing including an integrated actuator arm.

A further aspect of the disclosure is directed to a single axis solartracker including: a torque tube, a plurality of photovoltaic panelssupported by the torque tube. The single axis solar tracker alsoincludes a plurality of piers, configured to support the torque tube andthe photovoltaic panels; and a plurality of solar tracker bearingsincluding, at least one rotatable part, the rotatable part including anotch for receiving the torque tube; a slot, formed in the rotatablepart and extending below the notch, the slot defining an arc havingmultiple radii. The single axis solar tracker also includes at least oneengagement member configured to be received in the slot. The single axissolar tracker also includes at least one base configured to secure theengagement member in the slot and to secure the bearing to one of theplurality of piers.

Implementations of this aspect of the disclosure may include one or moreof the following features. The single axis solar tracker where the slotincludes a first radius at a bottom portion of the rotatable part, and asecond radius proximate at least one termination of the slot where thesecond radius is smaller than the first radius. The single axis solartracker further including a third radius proximate a second termination,where the third radius is larger than the first radius. The single axissolar tracker where the slot includes a first radius at a bottom portionof the rotatable part, and a second radius proximate at least onetermination of the slot where the second radius is larger than the firstradius. The single axis solar tracker where the slot includes a firstradius at a bottom portion of the rotatable part, and a second radiusproximate at least one termination of the slot where the second opposesthe first radius. The single axis solar tracker where the slot includesa third radius proximate a second termination, where the third radiusopposes the first radius.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and features of the present disclosure are describedhereinbelow with reference to the drawings, wherein:

FIG. 1 is a perspective view of a solar tracker in accordance with thedisclosure;

FIG. 2 is a perspective view of a bearing supporting a solar tracker inaccordance with the disclosure;

FIG. 3 is a plan view of a bearing in accordance with the disclosure;

FIG. 4 is a plan view of a bearing in accordance with the disclosure;

FIG. 5 is a plan view of a solar tracker in accordance with thedisclosure;

FIG. 6 is a perspective view of an actuation mechanism in accordancewith the disclosure;

FIGS. 7A and 7B are side views of an actuation mechanism and a bearingin accordance with the disclosure;

FIGS. 8A and 8B and 8C are side views of an actuation mechanism and abearing in accordance with the disclosure;

FIGS. 9A, 10A, and 11A are side views of rotatable parts of a bearingdepicting variations in their respective slots in accordance with thedisclosure;

FIGS. 9B, 10B, and 11B are side views of the rotatable parts of FIGS.9A, 10A, and 10C as they are rotated in a bearing as compared to arotatable part with a uniform radius slot in accordance with thedisclosure;

FIGS. 12A and 12B are side views of a rotatable part of a bearing with avariable radius slot formed of a composite of at least three radii inaccordance with the disclosure;

FIG. 13A depicts a side view of a rotatable part of a bearing where thenotch is shifted in the direction away from an actuator arm inaccordance with the disclosure;

FIG. 13B depicts the effect of shifting the notch in improving theclearance of the actuation mechanism as the rotatable part is moved to ahigh angle position in accordance with the disclosure;

FIGS. 14A-14G depict a bearing with two rotatable parts mounted on apier and an actuating mechanism mounted between the rotatable parts inaccordance with the disclosure; and

FIG. 15 depicts an alternative bearing employing a follower havingmultiple radii in accordance with the disclosure.

DETAILED DESCRIPTION

The present disclosure is directed to solar tracking systems. Moreparticularly, the disclosure is directed to a tracker support andbearing system for a single axis solar tracker employing a variableradius bearing.

FIG. 1 depicts a solar tracker 1. The solar tracker 1 includes a seriesof piers 2 for anchoring the solar tracker 1 in the ground. The piers 2may be anchored in for example by pilling, screwing, bolting,ballasting, or any other means allowing fastening and stabilizing thetracker support system to the ground. This solar tracker 1 includes amovable structure 3 rotatably mounted on the piers 2 around a horizontalaxis of rotation A (FIG. 3) and more specifically, rotatably mounted onthe upper ends of the piers 2.

The movable structure 3 includes one or more parallel rails, not shown,which receive photovoltaic panels 9. The photovoltaic panels 9 may befastened to the rails using a variety of fasteners and clamps as isknown in the art. The movable structure 3 also includes a horizontaltorque tube 10 to which the rails are connected, and which furthersupport the photovoltaic panels 9. The torque tube 10 is rotatablymounted to the piers 2 about the horizontal axis of rotation A and ismore specifically rotatably mounted on the upper ends of the piers 2inside bearings 4.

The torque tube 10 extends along a horizontal central axis B and is inthe form of a tubular beam of a square-shaped cross-section in theexample illustrated in the figures. Of course, other cross-sectionshapes for the torque tube may be considered, such as circular andrectangular sections, etc.

Each bearing 4 is identical and includes a rotatable part 5 and abracket 6 which secures the torque tube 10 in the bearing 5. A base 7 isused to secure the bearing 4 to the pier 2. Each bearing 4 includesengagement members 8. The engagement members 8 may be ball bearings,roller bearings, needle bearings, lubricious slides, or other types ofengagement devices that allow the rotatable part 5 of the bearing tomove relative to the engagement members 8.

The rotatable part 5 may be formed of a relatively thin plate of metalsuch as steel. The rotatable part 5 may also be formed of two metallicplates pressed and fastened to each other, for example by bolting,welding, riveting, etc.

The rotatable part 5 is generally semi-circular and includes a notch 12for receiving the torque tube 10. The rotatable part 5 also includesslot 14 presenting a semicircular arc of between 120° and 180°, inparticular between 150 and 170°. The slot 14 extends below the notch 12and rises at the sides on either side of this notch 12. Thus, the notch12 is located inside the inscribed imaginary circle centered on thehorizontal axis of rotation A and following the slot 14. Referring toFIG. 3, the slot 14 presents two opposite terminations 16, formingstoppers for the engagement members 8. A bracket 6 closes the notch 12of the rotatable part 5 and is fastened on this rotatable part 5 so asto clamp the torque tube 10 inside this notch 12.

As illustrated in FIG. 3, the notch 12 and the slot 14 are shaped sothat the horizontal axis of rotation A is located above the central axisB of the torque tube 10 and preferably so that the horizontal axis ofrotation A passes through the center of gravity G of the photovoltaicpanels 9.

The base 7 is composed of two folded metallic plates 18 forming lateralelements surrounding the rotatable part 5. Each plate 18 comprises anupper portion 20 pierced with two holes for fastening two engagementmembers 8. The upper portions 20 of the two plates 18 are disposed oneither side of the slot 14 of the rotatable part 5, and the engagementmembers 8 are fastened on these upper portions 20, between these upperportions 20 facing each other, for example via a bolt and nut setpassing both through the aligned holes of the upper portions 20 and theengagement members 8. Each plate 18 includes a lower portion 22 whichmay be pierced with holes for a fastening by bolting to a pier 2 orconfigured to be welded to a pier 2.

The engagement members 8 are mounted so as to roll or slide in slot 14and are interposed between these upper portions 20 which hold them inplace in the slot 14. Thus, when the solar tracker 1 rotates, therotatable part 5 pivots with the torque tube 10, this pivoting of therotatable part 5 relative to the fixed base 7 is enabled by and guidedby the contact of the engagement members 8 inside the slot 14 of therotatable part 5.

FIG. 5 depicts an end view of a single axis solar tracker 1 configuredwith an articulation system 100. The articulation system 100 is moreclearly depicted in FIG. 6 to include an actuator 102 and a gearbox 120.The actuator 102 includes a tubular body 106, a nut 108, a power screw110, and a heim joint assembly 112. Although generally illustrated ashaving a cylindrical profile, it is contemplated that the tubular body106 may include any suitable profile, such as square, rectangular, oval,hexagonal, etc. A heim joint assembly 112 is formed on one end of theactuator opposite the gear box 120.

An actuator mounting flange 42 is disposed on an outer surface of thepier 2 and is configured to enable a pin (not shown) or other suitablemeans for rotatably coupling a portion of the articulation system 100thereto. Specifically, the heim joint 112, formed at one end of thetubular body 106, is received in the mounting flange to secure thearticulation system to the pier 2.

The power screw 110 includes a thread form that is complimentary to thatof the nut 108 such that the power screw 110 may threadably engage thethreaded bore of the nut 108. In this manner, as the power screw 110 isrotated in a first direction, the overall length of the actuator 102increases and as the power screw 110 is rotated in a second, oppositedirection, the overall length of the actuator 102 decreases. Theincrease or decrease in the overall length of the actuator 102 causesrotation of the solar tracker 1.

The gear box 120 is connected via a shaft 114 to a drive motor (notshown). The shaft 114 enters the gear box 120 and is coupled via gearingin the gear box 120 to the power screw 110. Rotation of the shaft 114,by the drive motor results in rotation of the power screw to drive thesolar tracker 1 to a desired position. The gear box 120 may also includean output shaft which couples to the next gear box 120 of the solartracker 1. In this way a single drive motor can synchronously drive eachactuator 102 to move the entire length of the solar tracker 1.

As will be appreciated, incorporating the articulation system 100 andthe bearing 4 into a single solar tracker 1 can result in somechallenges. As depicted in FIGS. 7A and 7B, an articulation system 100is operably connected to a bearing 4 mounted on a pier 2. Because thesolar tracker 1 has just a single torque tube 10, an actuator arm 200 isrequired to provide a location to mount the gear box 120, and to providea moment arm to drive the torque tube 10 so that it rotates in thebearing 4 and therewith changes the orientation of the photovoltaicpanels 9. However, as depicted in both FIG. 7A and FIG. 7B if theactuator arm 200 is too short, there are interferences between the gearbox end of the articulation system 100 and the pier 2 at the high anglesof movement of the torque tube 10.

To address the interference issue, a longer actuator arm 200 may beemployed as depicted in FIG. 8A and 8B. Alternatively, the coupling ofthe actuator arm 200 to the torque tube 10 can be offset from thebearing 4 as depicted in FIG. 8C. However, these solutions havetrade-offs that can have a commercial impact. With respect to the longeractuator arms 200, this results in the need for a longer articulationsystem 100. This entails longer tubular body 106, longer power screws110 and potentially longer/taller piers 2 to accommodate the positioningof the mounting flange 42 at a lower position on the pier 2. Thismovement of the mounting flange 42 is necessary because of the increasedlength of the articulation system 100 when in the compressed position asseen in FIG. 8B.

With respect to offsetting the actuator arm 200 from the bearing 4 asdepicted in FIG. 8C, this too has drawbacks. A first drawback is that byoffsetting the actuator arm 200, the loads associated with the drivingof the solar tracker 1 are not centered on the pier 2. This offsettingcreates a variety of moments on the solar tracker 1 and induces twist toa variety of components of the solar tracker. Thus, to avoid thistwisting, with existing componentry the capacity of the solar tracker 1is reduced. Alternatively, the components can be upgraded to overcomethe twist and other issues, but with added cost making it a potentiallycommercial impossibility.

One aspect of the instant disclosure is directed to further alternativearrangements for the incorporation of the bearing 4 into the solartracker 1. One alternative is to change the shape of the slot 14 in therotating part 5 of the bearing 4. FIGS. 9A-11C depict a rotation part 5having three different shaped slots 14. By altering the shape of theslot 14, the movement of the solar tracker 1, is altered in comparisonto bearings 4 having a constant radius arc slot as depicted in FIG. 3.The results of these changes can be seen in FIGS. 9B, 10B, 11B, wherethe rotation of the rotatable part 5 having multiple radii is comparedto a rotatable part having a constant radius. In FIGS. 9B and 10B bychanging the radius of the slot 14 so that it is larger and the ends ascompared to a center portion of the slot 14, the rotatable part 5 of thebearing 4 actually moves horizontally away from the pier 2 on which thebearing 4 is mounted. In FIG. 11B, the opposite effect is observed, andthe rotatable part is drawn horizontally towards the pier 2.Accordingly, one aspect of the disclosure is directed to a solar tracker1 and particularly a bearing 4 having a rotatable part 5 with a variableradius slot 14 formed therein. The exact parameters of the variableradius slot 14 can depend on the application and the other componentsbeing employed in the solar tracker 1. As depicted in FIG. 9A, thevariable radius may simply be portion of the slot 14 towards theterminations 16 is formed with a larger radius the slot 14 at a bottomportion of the rotatable part 5. Alternatively, as depicted in FIG. 10A,the variable radius may take on a more sinusoidal shape and define anopposing arcs with opposing radii such that nearer the terminations theslot 14 is defined by an arc that opposes the arc at the bottom portionof the rotatable part 5. Still further, in FIG. 11A the slot 14 includesa radius proximate the terminations that is smaller than the radius atthe bottom portion of the rotatable part.

A further aspect of the disclosure is depicted in FIGS. 12A and 12Bwhere the shape of the slots depicted in FIGS. 9A and 11A and 10A and11A are respectively combined. As depicted in FIG. 12A the left side ofthe slot 14 has a shape which corresponds to that of FIG. 11A and theright side corresponds to that of FIG. 9A. Similarly, in FIG. 12B theleft side of the slot 14 corresponds to that of FIG. 12A while the rightside corresponds to that of FIG. 10A. This combination of profilesyields an arc of movement of the torque tube 10 as it rotates that placethe torque tube 10 predominately on one side of a centerline of the pier2 and the bearing 4 mounted therein the solar tracker's range of motionwhen compared to a constant radius. Because, the articulation system 100is connected to the torque tube 10 on just one side of the pier 2, andonly experience interference at the high angles of rotation of thetorque tube 10 on that side of the pier 2, the result is a slot 14 whichis beneficial in eliminating the interference without significantlyimpacting other aspects of the design of the solar tracker 1.

A further aspect of the disclosure is directed to the placement of thenotch 12 in the rotatable part. As depicted in FIG. 13A and 13B, thecenterline of the notch 12 can be offset to one side of the rotatablepart 5. As depicted in FIG. 13A the centerline of the notch 12 is movedaway from the actuator arm 200 and the location where the gear box 120and actuation system 100 are connected to the rotatable part 5. Thismovement of the centerline of the notch 12 helps in balancing the loadson either side of the bearing 4. As noted above, on the side of thesolar tracker 1 including the actuation system 100, there are gear boxes120, shafts 114, the actuator arm 200, and other components whichincrease the weight of the solar tracker 1 on that side of the bearing4. By shifting the centerline of the notch 12 in the direction of theactuation system 100, the moment arm of that side of the solar tracker 1is reduced, and that of the opposite side is increased. The result isthat solar tracker 1 is in fact more balanced than if the notch 12 werecentered in the bearing 4. Those of skill in the art will recognize thatthe actuator arm 200 of FIGS. 13A and B is an integrated actuator armformed as a single component with the rotatable part 5. Alternatively,the actuator arm may be a separate component secured to the rotatablepart 5, as depicted in FIG. 7A and 7B.

Further, another aspect of movement of the centerline of the notch 12 isthat the effective length of the actuator arm 200 is increased, but theactual length it extends from the rotating part 5 can be reduced inlength. Still further the clearance between the actuation system 100 andthe torque tube 10 is increased, particularly at high angularorientations as depicted in FIG. 13B. Though depicted in FIGS. 13A and13B as employing the rotatable part 5 of FIG. 11A, any of the variableradius rotatable parts 5 described herein may be employed in thisembodiment.

As depicted in FIGS. 9A, 10A, 11A, 12A and B and 13A and B, theeffective radius of the slot 14 changes as the rotatable part 5 rotatesrelative to the engagement members 8 (FIG. 3) which are held in place bythe upper portions 20 of the plates 18 mounted on the pier 2. The resultis a bearing 4 where the center of rotation is neither coincident withthe center of the torque tube 10 nor coincident with the center ofgravity of the solar tracker 1 through the entirety of the solartracker's rotation. While this may result in some unbalancing of thesolar tracker 1 at certain portions of the rotation of the solar tracker1, this unbalancing caused by the change in the center of rotation hasseveral benefits. As an initial matter, the unbalancing, which is causedby the change in radius of the slot 14, eliminates interference with theactuator 100 as depicted in FIGS. 7A and 7B. Second, in some situationsthe actuation systems 100 may be shortened resulting in a weight andtherefore power savings in the operation of the solar tracker 1.Further, the unbalancing allows for the shortening of the actuator arms200. Finally, the change in radius can achieve a reduction in thenecessary height of the pier 2.

Still a further aspect of the disclosure can be seen with reference toFIGS. 14A-14G. In FIGS. 14A-14G, a bearing 4 is depicted having tworotatable parts 5. Each pier 2 is affixed with at least one base 300.The base 300 includes two U-channels 302. The U-channels support a pairof engagement members 8 in each U-Channel. Each pair of engagementmembers 8 ride in a slot 14 of a rotatable part 5. The actuator arms 200of the rotatable parts are received on and connected to opposite sidesof a gear box 120. A gap 304 of approximately the width of the gear box120 separates the two rotatable parts. The gap 304 eliminatesinterference issues described in connection with FIG. 7A, while allowingthe actuation system 100 to remain centered on the pier 2. Further, asdepicted in FIGS. 14A-14G, the actuator arm 200 is integral with therotatable part 5, however, it may also be formed of an attachedcomponent as shown in FIG. 7A.

In operation the gap 304 allows for the gear box 120 to pass through thebearing 4 as the actuation system 100 moves from full extension asdepicted in FIGS. 14B and 14E to full retraction as depicted in FIGS.14C and 14G. In this way, the twisting and other detrimental forcesexperienced in the offset arrangement of FIG. 8C are eliminated.

The embodiment of FIGS. 14A-14G allows for the articulation system 100to employ shorter actuators 102. Further, the piers 2 can be reduced inheight, which reduces the overall height of the solar tracker 1. This inturn reduces the effects of wind loading experienced by the solartracker 1. Still further, the embodiment of FIG. 14A-14G reduces thenumber of large components in the solar tracker 1, including for examplethe mass of material for any one rotatable part 5, because the load onthe bearing 4 is now borne by two rotatable parts and two pair ofengagement members 8.

Though the bearing 4 is generally described herein as employing arotatable part 5 that includes a slot 14, it will be appreciated thatthe slot 14 is not required to achieve the benefits of the disclosureand other means of effectuating a multiple-radius bearing assembly 4 canbe achieved. As an example, rather than having two engagement members 8ride in the slot 14 (FIG. 3), a similar outcome can be achievedutilizing a follower 400 captured between, for example, four engagementmembers 8 as depicted in FIG. 15. The follower 400 may be mounted to thetorque tube 10 of the solar tracker 1. The follower 400 can have a shapewhich corresponds to anyone of the slots 14 depicted in FIGS. 9A-14G. Asthe actuation system 100 extends or retracts the follower 400 passesthrough the four engagement members 8 allowing the torque tube and solarmodules 3 mounted thereon to rotate. The follower 400 with the multipleradii forces the torque tube 10 to follow an arcuate path as force isapplied by the actuation system 100 to rotate the solar tracker 1.Following the change in radius of the follower 400, the center ofrotation of the solar tracker changes and results at points in anunbalancing of the solar tracker 10 as described above, and achieves thebenefits also described above. Though shown as a round bar, follower 400is not so limited and may be formed by a flange located on the rotatablepart 5 that is captured by the engagement members 8, or otherconfigurations known to those of skill in the art.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplifications of particular embodiments.

What is claimed is:
 1. A solar tracker bearing comprising: a firstrotatable part, the rotatable part including a notch for receiving atorque tube; a slot, formed in the rotatable part and extending belowthe notch, the slot defining an arc having multiple radii; a firstengagement member configured to be received in the slot; and at leastone base configured to secure the engagement member in the slot and tosecure the bearing to a pier.
 2. The solar tracker bearing of claim 1,wherein the slot includes a first radius at a bottom portion of therotatable part, and a second radius proximate at least one terminationof the slot wherein the second radius is smaller than the first radius.3. The solar tracker bearing of claim 1, wherein the slot includes afirst radius at a bottom portion of the rotatable part, and a secondradius proximate at least one termination of the slot wherein the secondradius is larger than the first radius.
 4. The solar tracker bearing ofclaim 1, wherein the slot includes a first radius at a bottom portion ofthe rotatable part, and a second radius proximate at least onetermination of the slot wherein the second opposes the first radius. 5.The solar tracker bearing of claim 2, further comprising a third radiusproximate a second termination, wherein the third radius is larger thanthe first radius.
 6. The solar tracker bearing of claim 2, furthercomprising a third radius proximate a second termination, wherein thethird radius opposes the first radius.
 7. The solar tracker bearing ofclaim 1, further comprising a second rotatable part including a notchfor receiving the torque tube.
 8. The solar tracker bearing of claim 7,wherein the second rotatable part comprises a second slot extendingbelow the notch and defining an arc having multiple radii, wherein theslot in the first rotatable part matches the slot in the secondrotatable part.
 9. The solar tracker bearing of claim 8, furthercomprising at least a second engagement member.
 10. The solar trackerbearing of claim 9, wherein the first and second engagement member arereceived in a U-channel supported by the base to secure the first andsecond engagement members in their respective slots in the respectiverotatable parts.
 11. The solar tracker bearing of claim 10, wherein thefirst and second engagement members each comprise two engagementmembers.
 12. The solar tracker bearing of claim 11, wherein each of thefirst and second rotatable parts include an actuator arm.
 13. The solartracker bearing of claim 12, wherein the first and second rotatableparts are separated from one another by a gap.
 14. The solar trackerbearing of claim 13, wherein the gap is configured to receive a gear boxof an articulation system.
 15. The solar tracker bearing of claim 1,further comprising a notch offset from a centerline of the rotatablepart.
 16. The solar tracker bearing of claim 15, further comprising anactuator arm.
 17. A single axis solar tracker comprising: a torque tube;a plurality of photovoltaic panels supported by the torque tube; aplurality of piers, configured to support the torque tube and thephotovoltaic panels; and a plurality of solar tracker bearingsincluding, at least one rotatable part, the rotatable part including anotch for receiving the torque tube; a slot, formed in the rotatablepart and extending below the notch, the slot defining an arc havingmultiple radii; at least one engagement member configured to be receivedin the slot; and at least one base configured to secure the engagementmember in the slot and to secure the bearing to one of the plurality ofpiers.
 18. The single axis solar tracker of claim 17, wherein the slotincludes a first radius at a bottom portion of the rotatable part, and asecond radius proximate at least one termination of the slot wherein thesecond radius is smaller than the first radius.
 19. The single axissolar tracker of claim 17, wherein the slot includes a first radius at abottom portion of the rotatable part, and a second radius proximate atleast one termination of the slot wherein the second radius is largerthan the first radius.
 20. The single axis solar tracker of claim 17,wherein the slot includes a first radius at a bottom portion of therotatable part, and a second radius proximate at least one terminationof the slot wherein the second opposes the first radius.